Reaction injection molding (RIM) is a one-shot injection method of liquid components usually by impingement into a closed mold where rapid polymerization occurs resulting in a molded plastic product.
The pressures employed are much lower than in conventional injection molding processes.
In a RIM process, the viscosity of the materials fed to a mold is about 50 to 10,000 cps, preferably about 1500 cps, at injection temperatures varying from room temperature for urethanes to about 150.degree. C. for lactams. Mold temperatures in a RIM process typically range from about 100.degree. C. to about 220.degree. C. The mold pressures generally range from about 1 bar to 100 bar, more particularly 1-30 bar. At least one component in the RIM formulation consists of monomers and adducts thereof that are polymerized to a polymer in the mold.
RIM differs from injection molding in a number of important respects. The main distinction between injection molding and RIM resides in the fact that in RIM, a chemical reaction takes place in the mold to transform a monomer or adducts to a polymeric state. Injection molding is conducted at pressures of about 700 bar to 1400 bar in the mold cavity by melting a solid resin and conveying it into a mold maintained at room temperature and the molten resin at about 150.degree. C. to 350.degree. C. At an injection temperature of about 150.degree. C. to 350.degree. C., viscosity of the molten resin in an injection molding process is generally in the range of 50,000 cps to 1,000,000 cps and is typically about 200,000 cps. In injection molding processes, the solidification of the resins occurs in about 10 to 90 seconds, depending on the size of the molded product. Subsequently, the molded product is removed from the mold. There is no chemical reaction taking place in an injection molding process when the resin is introduced into a mold.
For practical purposes, in a RIM-process the chemcal reaction must take place rapidly in less than about 2 minutes for smaller items. Presently, urethanes are commercially available for RIM processing although systems based on nylon and epoxy are said to be in development.
In connection with nylons in general, the following developments of the anionic polymerization nylon are broadly germane.
Polymerizing a lactam to obtain a nylon has been known for many years.
In U.S. Pat. No. 3,018,273 a process for the in situ polymerization of caprolactam is described. An organomagnesium compound is used as an initiator and an N,N diacyl compound is used as promoter (or activator).
British Pat. No. 1,067,153 describes a process for preparing nylon-block-copolymers by anionically polymerizing caprolactam in the presence of various activators suitable for preparing nylon 6 polymers. Preparation of nylon block copolymers using an isocyanate terminated polypropylene glycol and a potassium based catalyst is described. A nylon block copolymer containing at least one polyether block is thereby formed.
In U.S. Pat. Nos. 3,862,262, 4,031,164, 4,034,015 and 4,223,112 various aspects of the preparation of nylon block copolymers from caprolactam in the presence of an acyllactam activator are described.
U.S. Pat. Nos. 4,031,164 and 4,223,112 describe lactam-polyol-polyacyl-lactam-block terpolymers having a specified ratio of the various components. More particularly, the former patent discloses the use of 18 to 90% by weight of polymer blocks in the terpolymer.
U.S. Pat. No. 3,862,262 describes lactam-polyol-acyl-polylactam block-terpolymers.
U.S. Pat. No. 4,034,015 is directed to lactam-polyol-polyacyl-lactam or lactam-polyol-acyl-polylactam block terpolymers having at least about 5% ester end group termination.
Reissue Patent 30,371 describes preparing polyester-polyamide compounds by condensation of an alcohol and acyllactams in the presence of at least one Group IA, IIA, IIB, and IIIA metal or metal compound.
U.S. Pat. No. 3,925,325 describes the preparation of monomeric and/or polymeric compounds such as esters, polyesters, ester amides, and polyester-polyamides by conducting the the reaction of an imide and an alcohol in the presence of an organoaluminium, imide-alcohol condensation catalyst.
U.S. Pat. No. 3,965,075 describes using an amide or a Group IVA, IB, IVB, VB, VIB, or VIII organometal compound for this condensation.
In European Patent application No. 67693, now laid open to public inspection, acid halide materials and acyllactam functional materials are described as useful in the preparation of nylon block copolymers selected from the group consisting of those having the formula ##STR1## and ##STR2## wherein A is X or Q,
X is halogen, ##STR3## with EQU Y=C.sub.3 -C.sub.11 PA1 b.sub.i is an integer.gtoreq.2, PA1 polybutadiene polyol PA1 polyester polyol containing one or more polyether blocks PA1 grafted polyether polyol,
alkylene;
a is an integer equal to 1, 2 or 3;
b is an integer equal to or greater than 2;
R is a di- or polyvalent group selected from hydrocarbon groups and hydrocarbon groups containing ether linkages; and
Z is a segment of:
(1) a polyester having a minimum molecular weight of 2,000, PA0 (2) a polyester containing polyester segments having minimum molecular weights of about 2000, PA0 (3) a segment of a hydrocarbon or PA0 (4) a polysiloxane.
European patent application No. 67,695, now laid open to public inspection, describes a process for preparing a nylon block copolymer by reactively contacting a lactam monomer, a basic lactam polymerization catalyst and the acyllactam functional material described in European patent application No. 67,693.
European patent application No. 67,694, now laid open for public inspection, is directed to acid halide and acyllactam functional materials and to a process for the preparation of nylon block copolymers therewith. The acid halide or acyllactam functional materials are selected from the group defined by a complex formula.
Sibal et al, Designing Nylon 6 Polymerization Systems for RIM', apparently presented in part at the 2nd International Conference on Reactive Polymer Processing, Pittsburgh, Pa., in November 1982, describes preparing various initiators for anionically polymerizing lactams including a polymeric initiator. This initiator is prepared by reacting hexamethylene diisocyanate (HDI) with a polypropylene oxide diol having an average molecular weight of 2000, by slow addition of the polyol (1 mole) to two moles of HDI. The resulting product was reacted with anhydrous lactam at 80.degree. C. No mechanical properties data are reported on the final product. Indeed, further work is said to be required to even begin exploring the processability and properties of the products. This paper also reports that reaction ratios and other process governing parameters are not known and further work is required.
U.S. Pat. No. 4,400,490 describes the anionic polymerization of a lactam with an epoxy-compound in the presence of a basic catalyst and a promoter. The epoxy compound can be the reaction product of a polymeric polyol and an epoxy compound.
U.S. Pat. No. 3,793,399 describes the use of a polyol, soluble in molten caprolactam, for improving the impact resistance of polycaprolactam. An organic nitrogen compound is used as a promoter in the polymerization.
The use of etherified polyols in the anionic polymerization of caprolactam is described in U.S. Pat. No. 3,770,689.
It has been suggested to prepare an activator for the polymerization of lactam by reacting a polyol (such as a polymeric diol, triol or tetrol) and a lactam terminated polyisocyanate in the presence of a lactam polymerization catalyst of a Lewis acid.
Presently, nylon 6 block copolymers may be candidates for structural exteriorly exposed panels. However, drawbacks weighing against the adaptability of nylon to the RIM process include the high moisture absorption rate of the product which could adversely affect dimensional stability between demolding and coating operations. Thus, mechanical properties such as impact strength--especially for the glass fiber filled products--, water absorption, and flexural modulus must be improved. Otherwise, there will be obstacles to production on a commercial scale.
Another disadvantages of the RIM process for the preparation of nylon block copolymers is that it is not possible to determine the molecular weight (or degree of polymerization) of the nylon blocks independently from the amount of rubber phase used and the molecular weight thereof.
In the anionic polymerization of a lactam, using a polymeric activator, only two degrees of freedom exist, viz. when the molecular weight of the initiator and the amount thereof (=rubber content) have been fixed, the degree of polymerization is also fixed and vice versa. It would be very advantageous if the amount of rubber phase incorporated in the system could be independent of the molecular weight of the nylon block in the nylon block copolymer.
The improvement of the properties mentioned herein above, and other objects are achieved by the present invention.